The production of cast metal brake drums for heavy-duty vehicle wheels begins with a conventional sand-patterned mold casting operation. After cleaning, the raw cast brake drums are precision drilled and concentrically machined to dimensional tolerances determined by extrinsic factors of vehicle design. The wheels, axles and braking system each affect the "design dimensions" of a finished cast brake drum. However, it is well known to each of the several engineering disciplines providing factors involved in design of vehicles that a finished cast brake drum with useable "design dimensions" may or may not have a "final balance" which is acceptable for vehicle operation under dynamic or a range of road conditions and vehicle speeds.
The present invention relates to a system, method or process which will use conventional and relatively inexpensive factory machines for final balancing of a cast metal brake drum by cutting away a crescent or wedge of the cast material from the drum squealer band or any outside drum surface which is cylindrical, conical or subtantially perpendicular relative to the designed center or rotational axis of the drum.
The scope and content of the prior art has been determined as explained below.
The following United States patent references have been identified as broadly disclosing removing material that causes an imbalance from a work piece after having determined the area to be displaced:
U.S. Pat. No. 1,731,922, Eaton, Oct., 1929. (balancing rotors, such as armatures of dynamo-electric machines); U.S. Pat. No. 2,690,075, Kryeske, Sept., 1954. (a rotating body is dynamically balanced by relocating its center of rotation); U.S. Pat. No. 2,731,887, Sjoestrand, Jan., 1956. (balancing a rotatable body by removing material from the heaviest side or applying material to the lightest side); U.S. Pat. No. 2,792,725, Lannen, May, 1957. (machine for balancing a circular work-piece 16 using a drilling unit 70, 71, 72); U.S. Pat. No. 2,937,613, Larsh, May, 1960. (a dynamic balancing machine which eliminates the need for any instrument which measures the magnitude of the unbalanced condition); U.S. Pat. No. 3,295,413, De Castelet, Jan., 1967. (a French invention, an engine crankshaft balancing installation using a "want-of-balance" measuring machine positioned along a crankshaft transfer path); and, U.S. Pat. No. 4,545,021, Suzuki, et al., Oct., 1985. (a Japanese invention, a seven-step (a) through (g) method for correcting dynamic unbalance of an electric motor rotor). This investigation was conducted within Class 73, subclasses 66, 459, 460, 461 and 487.
Other United States patent references were identified in Class 82, subclasses 1C, 2A*, 4A*, 8, 38A and Dig. 8*, and Class 188, subclass 218A. U.S. Pat. No. 4,586,407, Nall, May, 1986 discloses the use of lathe-type machine tools for machining cylindrical or tubular work-pieces to remove axial peripheral irregularity and refers to conventional lathe-type machines with an incrementally adjustable tangent cutting tool. U.S. Pat. No. 4,656,896, Bietz et al., April, 1987, a French invention, relates to a digitally controlled lathe and a radially adjustable chuck axis for the parts to be machined. U.S. Pat. No. 4,366,543; Feller, et al., Dec., 1982, discloses method and apparatus for the out-of-round machining of work-pieces (piston rings) with numerically or electronically programmable memory for controlling the radial feed of a cutting tool 6.
U.S. Pat. No. 3,076,363, Hack, Feb., 1963; U.S. Pat. No. 3,691,880, Ratteree, et al , Sept., 1972; U.S. Pat. No. 4,215,603, Jones, Aug., 1980; and U.S. Pat. No. 4,455,900, Callanan, et al., June 1984, each disclose machining work-pieces including brake drums.